The same user may have a plurality of communication devices able to receive such messages, for example various terminals each provided with a screen, such as personal computers, portable or otherwise, mobile telephones or personal digital assistants, as well as other terminals with no screen but able to reproduce messages in sound form only or in any other non-text form. These various terminals will then most often be connected individually to the message base, either directly or via one or more cable or other communication networks, and thus have individual access to its content.
Thus if such a user uses one terminal to modify the content of the message base or the status of one or more of the messages contained therein, that user's other terminals will in theory remain unaware of the modification, and there is therefore the risk of those other terminals offering an out-of-date view of the content of the message base.
Thus if a message included in the base is read by the user by means of a first terminals only that terminal will retain a trace of that action, and so other terminals of that user will show said message as unread, therefore unnecessarily attracting the user's attention, who will potentially waste valuable time re-reading at least part of said message before realizing it had already been read.
To alleviate such drawbacks, some electronic messaging services use means having the essential function of placing the message base in a centralized position and conferring on its content a reference quality for any terminal that has been caused to connect to it, each terminal then downloading the content of the message base during connection initialization. In such messaging services, different terminals can therefore still have disparate contents, and in principle all that is achieved is that, following a connection to the message base by means of a given terminal, said given terminal will show the content of that base to the user reliably.
In order for each of the user's terminals to reproduce the content of the message base relatively reliably, automatic and periodic triggering of simultaneous downloads of said content into storage means in each of the terminals has been envisaged in the prior art, but such indiscriminate downloading of the entire content of the base generates a large volume of traffic via one or more networks of limited bandwidth, only to achieve a result that is not entirely satisfactory because the various representations of the content of the message base offered by the various terminals are identical only immediately after such simultaneous downloads have been effected.